Zinc is an essential trace metal in human nutrition. It is present in high concentration in animal and human ocular tissues. Zinc apparently has a variety of functions, including serving as an essential constitutent of zinc metalloenzymes. Pathological process and exposure to chelating drugs or chemicals may damage the eye by adversely affecting zinc metabolism. In addition zinc deficiency in human diet has adversely affected vision. We have studied dietary zinc deficiency in male Sprague-Dawley rats and have observed the accumulation of electron dense inclusion bodies in the retinal pigment epithelium (RPE). RPE cells and photoreceptor outer segments (OS) subsequently undergo severe degeneration. We thus propose a series of experiments to define the mechanisms of these pathologic changes. Our aims are: a) to determine whether the morphological alterations are produced in the RPE and OS of either weanling or adult pigmented rats (Long Evans) under the same experimental dietary conditions that affected albinos; d) to measure the concentration of zinc by means of atomic absorption spectrophotometry in ocular tissues of zinc-deficient Sprague-Dawley rats compared to normal diet controls; c) to determine whether zinc deficiency affects circulating serum vitamin A levels using fluorometric methods; d) to evaluate by light and electron microscopic autoradiography whether there is a modification or alteration of the binding of serum retinol-binding protein (SRBP) on the choroidal surface of the RPE cells of zinc-deficient rats; e) to analyze biochemically the inclusion bodies seen in the RPE of zinc-deficient rats; f) to examine the level of rhodopsin and visual cycle retinoids in the eyes of light- and dark-adapted zinc-deficient rats; and g) to determine whether the morphological changes seen in the RPE and OS of zinc-deficient animals are reversible with zinc resupplementation. Rats on controlled zinc dietary intake may provide useful as models for studying pathological processes in retinal dystrophies, nutritional requirements of the eye, and the effects of cation replacement.